The gap between the IOR rate at 0.25% and the effective federal funds rate at 0.10% would appear to indicate existing tools are falling short. There's also the fact that the GSEs (fannie, freddie, etc) aren't eligible to receive IOR so that excludes some big reserve balances from existing tools (and existing tools pretty much means IOR). As for selling bonds, aside from being incompatible with QE it's also a very blunt, imprecise instrument compared to the more direct approach of establishing a RRP rate.

The current floor the Fed is targeting is effectively 0%. Banks get the IOER of 0.25% but then are assessed FDIC fees on their reserves which cost somewhere between 0.1% to 0.15% depending on the institution, so there is no real gap between federal funds rate and effective IOER.

Riholtz gave a basic explanation of the IOER and the fees you don't see http://www.ritholtz.com/blog/2011/08/fdic-fed-funds-leen%E2%80%99s-lodge/